1. Field of the Invention
The present invention relates to a mobile telecommunication system, more particularly, to a repeater having frequency conversion in a mobile telecommunication system for generating a dummy frequency assignment signal for repeating a frequency conversion or providing a hard handoff based on a traffic signal having traffic and overhead information.
2. Prior Art
In a code division multiple access(CDMA) mobile telecommunication system, a repeater is used to embody a smooth communication environment and to enlarge coverage thereof. Since the cost of such a repeater is relatively small according to equipment investment and management and is easily installed, it is widely used to enlarge coverage in a wave shadow area such as a mountainous district or a large size building, in a weak wave area such as a subway, or in an area in which service is provided.
A typical repeater amplifies and transmits a weak signal generated by a mother base station. Since a repeating frequency between a base station and a repeater is identical with a service frequency, an oscillating phenomenon is generated in the repeater. Therefore, in order to prevent the oscillating phenomenon, an isolation device should be provided. However, up to now, since service has been performed in a low gain of the repeater, it is limited to enlargement of coverage.
Currently, in order to improve any limitation according to enlargement of coverage, a frequency converting repeater is being widely used. Such a frequency converting repeater receives a dummy frequency assignment signal transmitted from a mother base station and converts it into a traffic signal of the mother base station. Thus, the frequency converting repeater provides service to a wave shadow area or a weak wave area by means of the traffic signal so that an oscillating phenomenon which is generated in a conventional repeater can be prevented.
U.S. Pat. No. 3,750,173 (issued to Norbert E. Tackman on Jul. 13, 1973) discloses a frequency translating repeater using single-sideband techniques.
FIG. 1 shows a conventional frequency converting apparatus in a base station.
The conventional frequency converting apparatus includes a traffic frequency device S1, a dummy frequency assignment device S2, a linear power amplifier(LPA) 122, and a low noise amplifier(LNA) 128.
The traffic frequency device S1 includes a first channel card 102, a first analog conversion unit(ACU) 104, and a first baseband combiner and radio(BCR) 106. The first channel card 102 generates a digital traffic signal of a baseband having traffic information and overhead information. The overhead information includes pilot channel information, paging channel information, and sync channel information.
The first ACU 104 converts the digital traffic signal of a baseband from the first channel card 102 into an analog signal. The first BCR 106 converts the analog traffic signal of a baseband from the first ACU 104 into an intermediate frequency traffic signal and converts the intermediate frequency traffic signal into a forward traffic signal F1.
The dummy frequency assignment device S2 includes a second channel card 112, a second ACU 114, and a second BCR 116. The second channel card 112 generates a digital dummy frequency assignment signal of a baseband having overhead information. The second ACU 114 converts the digital dummy frequency assignment signal of a baseband from the second channel card 112 into an analog signal. The second BCR 116 converts the analog dummy frequency assignment signal of a baseband from the second ACU 114 into an intermediate frequency signal and converts the intermediate frequency signal into a forward dummy frequency assignment signal F2. The LPA 122 amplifies the forward traffic and dummy frequency assignment signals F1 and F2 from the first and second BCR 106 and 116, respectively, and transmits them through an antenna 124. Accordingly, both the traffic signal F1 and dummy frequency assignment signal F2 from the LPA 122 are transmitted through a first antenna 122 to thereby perform a hard handoff between frequency assignments of base stations. The LNA 128 low-noise amplifies reverse traffic and dummy frequency assignment signals F1 and F2 transmitted through an antenna 126 and outputs them to the first and second BCRs 106 and 116.
However, in the conventional frequency converter in a base station, in order to provide a dummy frequency assignment signal which has the same information as that of traffic frequency signal and has a frequency different from that of the traffic frequency signal, a channel card, an analog conversion unit, and a baseband combiner and radio for providing the dummy frequency assignment signal should be added. Accordingly, that requires additional expenses.